1. Field of the Invention
The present invention relates to a magnetoresistive element and a manufacturing method thereof, e.g., a magnetoresistive element capable of recording information by supplying an electric current in two directions, and a manufacturing method thereof.
2. Description of the Related Art
A magnetic random access memory (MRAM) using a ferromagnetic material is expected as a nonvolatile memory that achieves a high-speed operation, large capacity, and low power consumption. The MRAM includes a magnetic tunnel junction (MTJ) element using the tunneling magnetoresistive (TMR) effect as a memory element, and stores information in accordance with the magnetization state of this MTJ element.
In the conventional MRAM in which data is written by a magnetic field generated by a line electric current, the coercive force increases as the size of the MTJ element decreases. This often increases an electric current necessary for data write. In this conventional MRAM, it is difficult to achieve a small cell size for obtaining a large capacity and a low electric current at the same time.
A spin injection MRAM using the spin momentum transfer (SMT) write method as a write method for solving the above problem has been proposed. In this spin injection MRAM, information is written by directly supplying an electric current to the MTJ element, and changing the magnetization direction in a free layer in accordance with the direction of the electric current. Also, an MTJ element comprising two fixed layers sandwiching the free layer can increase the spin torque. This makes it possible to reduce the critical current density of the MTJ element.
When forming an MTJ element like this, a double magnetic tunnel junction is separated into MTJ elements in an etching step. However, the reaction product formed by etching during junction separation adheres to the side surfaces of the element, and shortcircuits the free layer and fixed layer. To avoid this shortcircuit of the free layer and fixed layer, taper etching can be performed. However, the processed sectional shape becomes a tapered shape, and the increase in etching film thickness caused by the two fixed layers increases the processing conversion difference during taper etching. This increases the MTJ element size.
As a related technique of this kind, the structure of a magnetoresistive effect element having inclined side surfaces is also disclosed (Jpn. Pat. Appln. KOKAI Publication No. 2003-298145). This magnetoresistive effect element has a magnetic domain structure that is stable even when the element size decreases.